Suspension of incandescent filaments



2. I, l AIl E s. R. MULLARD SUSPENSION OF INCANDESCENT FILAMENTS FiledOct.

ec, G, R924.I

Patented Dea 16, i924o narran STATES islam PATENT omnes.

STANLEY ROBERT MULLIi-ARD, F HAMMERSMITH, LONDON,v ENGLAND, ASSIGNOR TOTHE MULLARD RAIDIO VALVE COMPANY LIMITED, OF-HAMMERSMITH, LONDON,

ENGLAND.

SUSPENSION 0F INCANDESCENT FILAMENTS.

. l@ which the following is a specification.

This invention relatesy to the method of and means for supporting oranchoring filaments and particularly for supporting the lamentarycathodes of thermionic valves or il@ electron discharge tubes whichoperate at incandescence.

lt is the chief purpose of the present invention to ensure that thetension of such filaments will have the most suitable value 2@ and toenable the operative to judge with accuracy the correct amount oftension.

Broadly delined, the present invention consists in supporting a filamentin such a manner that it is placed in tension by means of the stress ina spring arranged so that its stress may be readily gauged, preferablyby a visual indication, by the operative. It is preferredto employ ahelical tension spring which is secured to one end of the filament inthe case of a straight filament, or to the bight in the case of ahair-pinlament. Y

One object of the invention consists in the provision ofa gauge orindicator which is fixed Within the bulb of the valve or other device insuch a position that when a point on the anchoring spring bears acertain relation to the gauge, the tension on the {ilament is at itsmost suitable value. Such a gauge may be calibrated to correspond todiii'erent amounts of tension, but this will not usually -be necessary.

According to one embodiment of the presy ent invention, the gauge maycomprise a rigidly supported Wire pointer so arranged that when thehelical tension spring sup- .porting the filament extendslongitudinally, va polnt on the spring or other movable ele-nlmentassociated with it comes oppositel a point on the, gauge.

Such a gauge may. be xed to the glass or quartz stem whichV supports oneor more electrodes 'of thevalve and lmay lcomprise opposite wiresextending parallel to the stem, or a single wire with its end turned atis located. Thefend of such tubular extenva member whichmoveswhen thespring is right angles to the stem, or again the gauge may be anextension of the stem and formed of glass-or quartz. Such extension maybe,v

a projection on one side, or may be a tubular extension within which thetension spring sion may serve as the gauging mark, or one or more marksmay be placed on the tubular extension. Again, in the case of athreeelectrode tube the gauge may be supported by the grid electrode ofthe tube.

Another useful embodiment of the invenp tion is furnished with means forpreventing the tension spring from extendin beyond a certain limit, thetension on the lament at that limit being of just the required amount.ln this form a bu'erA rigidly supported on the stem of the tube isarranged so that when the spring is extended suiliciently, it comes intocontact with the buffer which prevents any further expansion. This bu'ermayV consist of a wire carrying a central eye or a disc furnished with acentral hole through which passes the straight wire between the portionof the spring nearest the filament and the end of the filament. Such eyeor hole allows the straight wire to slide through, but prevents thehelical sprin from bein stretched beyond the desire v amount. gain aflexible wire may be con` nected between the two ends of the tension 85spring. Before the spring is extended the wire would be slack, but asthe spring is drawn out the said wire would straighten and preventy thespring extending beyond the length of the wire. Instead of a tensionspring, compression springs or other forms of spring may be employed. lnthe case of a compression spring, it may be enclosed in aftube attachedto the stem at one end and having a constricted opening at the other.Through this opening passes the shank of the hook to which the filamentisattached. Thel portion-of the'shank inside the tube passes through themiddle ofthe spring and ends in a cupshaped pistonv'fhch'` presses onthe end of' thev spring remote 'from the 4filament and compresses thespring. The compression of the spring is adjusted as before by notingthe relative position of a point on i l105 stretched with' relation to astationary point. The invention is particularly 'useful when a spring isemployed enclosed in an insulated4 readily appreciated from thefollowing description of some embodiments of the invention kwhen takenin conjunction with the anneXed drawings, in the various figures ofwhich the same reference numerals refer to corresponding parts. In thesedrawings Figure 1 is a view of a three electrode thermionic valve orelectron discharge tube, having the cathode supported in accordance withthe present invention;

Figure 2 shows the stem and f}ament hook of a modified embodiment;

. Figures 3, 4, 5, 6 and 7 are similar views of further embodiments.

Referring first to Figure l1, the bulb 1 is furnished with a lower stem2 upon which is carried the cylindrical anode or plate 43 and whichcarries the lower hook 4 for the filamentary cathode 5 'Ihe upper stem 6supports the grid electrode 7 and two anchor.

hooks or leading-in wires 8, 9, for the ends of the filament 5, which inthis example is of hairpin shape. 'Ihe spring 10 is a helical tensionspring and its lower end is anchoredy by being passed through the uppertubular end of the stem 2 and then bent outwards through a smallaperture 11 in that stem. The upper end of the spring 10 is connected toa link 12 preferably ofmolybdenum and preferably of larger diameter thanthe spring 10 in order to prevent the latter from being over-heated. Thelink 12 is turned over at its upper end to form the hook 4 to which thefilament is attached.l A wire 13 is fixed to the upper projection of thestem 2 so that its free ends project beyond the end of the springtowards the lilament 5. While the lower vseal of the valve issoft, thestem 2 is pulled downwards stretching the spring 10 until the uppermostturn of the-,spring 10 is 1 in line with the tips of the wire 13. Theends of the latter are made of such a length that when the spring 10 isso stretched it imparts the correct tension to the lilament 5. The

spring 10 may also be stretched by pulling the filament seal upwards atthe upper end of the valve whilst the seal is still soft.

In the embodiment illustrated in Figure 2, only o ne end of the wire 13is employed andl this is bent'inwards and is of such a length that thetop of the helical spring 10 just touches it when the correct tension isapplied.

In the embodiment shown in Figure 3, the gauge 13 is in the form of aglass or silica lug, according to the material of the stem, the gauge 13being an integral part thereof.

In another4 embodiment of the invention shown in Figure 4, the gauge 13takes the form of a wire attached to, or an extension of the grid 7.

Figure 5 shows another construction in which the upper end 14 of thestem 2 is made tubular to accommodate the spring 10. In this case theheight of the tubular part is so Iarranged that when the top of thehelical spring 10 is level with the top of the tubular part 14, thecorrect tension is applied to the filament. If desired, however, thepart 14 could be made longer and could bear a mark to which the top ofthe helical spring that its upper turn reaches the loop 15, the

'tension is correct.

In Figure 7 is shown a modied form showing the use of a compressionspring 16. This spring is enclosed in a tube 17 attached to the upperend of the stem 2, said tube being provided with inwardly turned lugs 18which are adapted to hold the spring 16 inside the tube` 17. The link 12passes centrally through the compression spring 16 and at its lower endis attached to the lowermost coil of the spring 16. The compression ofthe spring 16 is adjusted as hereinbefore described by noting therelative position ofthe lowermost coil of thespring, for example,`

with relation to a fixed point on the tube.

I-Iaving thus described myinvention what I claim as new and desire tosecure by Letters Patent is 1. In combination a lament, means for fixingone end of said filament, a xed gauge and a spring connected to anotherpoint. 1n said filament and stressed until a predeter# mined point insaid spring bears a definite relationship to said gauge.

2. In combination, a bulb, a filament having one end fixed in relationto said bulb, a fixed gauge and a tensionspring in the form of a helixfixed to another pointin said filament and stretched until the end turnof the helix is in alinement with said gauge. A

3. In combination, a bulb, a filament mounted in said bulb with one endfixed in relation to said bulb, a stem in said bulb, a gauge supportedupon said stem and comprising a member with an eye, a spring fixed toanother point in said filament and stretched to tension said filamentuntil the insieme spring contacts with said gauge adjacent the eyethereof. 4

4. An incandescent filament device, com-- prising a bulb, a hairpinlament therein having both of its ends fixed in relation to said bulb, astem secured to said bulb opposite the bight of said filament, a gaugecomprising a xed member projecting outwards from said stem and a helicaltension spring anchored at one end to said stem and at the opposite endto the bight of said/filament and stretched until a predetermined pointin said spring is in alinement with said gauge.

5. A thermionic valve comprising a bulb having stems at opposite partsthereof, two hooks projecting from one of 'said stems, a hairpinfilament having its ends xed to said hooks, an anode and grid supportedupon said stems, a gauge fixed to the stem-opposite said hooks and atension spring in the form of a helix anchored to said last-ned stem andto the bight of said filament and stretched until the outer turn of thehelix comes into alinement with said gauge.

6. Means for anchoring a filament coniprising a stem with a gaugeconsisting of a Wire fastened to the stem and bent to have a portion atright angles to the axis of the stem with an eye concentric with thestem, a tension spring in the form of a helix fastened to Said stem atone end and at the other end formed as a hooked shank passing throughsaid eye and engaging the bight of the filament, said spring beingstretched until the turn ofthe helix nearest the filament comes into'contact with said gauge.

STANLEY ROBERT MULLARD.

